Metal‐Free, Base‐Promoted, Tandem Pericyclic Reaction: A One‐Pot Approach for Cycloheptane‐Annelated Chromones from γ‐Alkynyl‐1,3‐Diketones

Abstract

A microwave-assisted, base-promoted, tandem cyclization reaction strategy has been developed for the synthesis of cyclohepta[b]chromones and spiro cyclohepta[b]chromones. Readily accessible γ-alkynyl-1,3diketones undergo intramolecular cyclization and 7-endo-trig carbocyclization to afford various cycloheptaneannelated chromones in one-pot reactions. This metal-free protocol also led to the generation of polycyclic ring with a new CÀ C bond and a new CÀ O bond.

Site‐Selective (Z)‐α‐Borylalkenyl Copper Systems for Nucleophilic Stereodefined Allylic Coupling

“…[17] Interestingly, compounds 28 and 29 were transformed, under identical conditions, into cyclic products 33 and 34, suggesting a [1,3]-hydrogen shift/ HBr elimination followed by base assisted pericyclic reaction (Scheme 5). [18] The enyne cycloisomerization mechanism is justified by the concomitant aromatization. The protodeboronation step in products 33 and 34 seems to be precluded suggesting a more stable Bpin moiety when is coordinated to the aromatic system.…”

Cinchona-Alkaloid-Derived NNP Ligand for Iridium-Catalyzed Asymmetric Hydrogenation of β-Keto Ester

“…Known compound . The product was purified by silica gel chromatography [50:1 (v/v) petroleum ether/ethyl acetate] as a yellow oil (1.46 g, 79% yield).…”

“…Known compound. 26 The product was purified by silica gel chromatography [50:1 (v/v) petroleum ether/ethyl acetate] as a yellow oil (1.46 g, 79% yield). 1 H NMR (600 MHz, CDCl 3 ) δ 12.52 (s, 0.07H, enol form), 7.81 (d, J = 6.0 Hz, 1H),7.43−7.45 (m, 1H), 6.95−6.97 (m, 1H), 6.90 (d, J = 6.0 Hz,1H), 5.97 (s, 0.07H, enol form), 3.91 (s, 2H), 3.83 (s, 3H), 3.79 (s, 0.21H, enol form), 3.73 (s, 0.21H, enol form), 3.65 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 192.9, 174.0 (enol form), 168.9 (enol form), 168.…”

Site‐Selective (Z)‐α‐Borylalkenyl Copper Systems for Nucleophilic Stereodefined Allylic Coupling

“…Interestingly, compounds 28 and 29 were transformed, under identical conditions, into cyclic products 33 and 34 , suggesting a [1,3]‐hydrogen shift/HBr elimination followed by base assisted pericyclic reaction (Scheme 5). [18] …”